Signal filtering and signal processing apparatus and method

ABSTRACT

A signal processing method, a signal filtering apparatus, and a signal processing apparatus are provided. An input signal may be input into a filter having a passband, a superfluous signal of the passband may be output from the filter, and a target signal may be obtained by subtracting the superfluous signal from the input signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.16/512,890 filed on Jul. 16, 2019 which is a continuation of U.S. patentapplication Ser. No. 15/349,230 filed on Nov. 11, 2016, now U.S. Pat.No. 10,382,074 B2, which claims the benefit under 35 USC § 119(a) ofKorean Patent Application No. 10-2015-0174790, filed on Dec. 9, 2015, atthe Korean Intellectual Property Office, the entire disclosure of whichis incorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to a signal processing and signalfiltering method of subtracting a noise signal.

2. Description of Related Art

Due to the population getting older, increasing medical costs, and adearth of personnel engaged in special medical services, research isbeing conducted on information technology (IT)-healthcare convergencetechnology in which IT is applied to medical technology. Due toimprovement in the IT-healthcare convergence technology, monitoring ahealth condition of an individual may be done anywhere the individualgoes in daily life, such as, for example, at home and work. Withimprovement in technology in the mobile healthcare field, a healthcondition of a moving user may be monitored anywhere and at any time.

An application for mobile healthcare may monitor a health condition inan environment in which a user moves and may operate based on a mobiledevice, such as, for example, a wearable device, thereby increasing theuser's convenience. The wearable device may have limitations ofperformance of an individual sensor, amount of power used, and size ofproduct, compared to a specialized non-wearable medical device. Suchlimitations may cause a signal to noise ratio (SNR) of a biosignalmeasured from the wearable device to deteriorate. Thus, the wearabledevice may require a low complexity technology for stably processing anoise signal in addition to the bio-signal.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, there is provided a signal processing methodincluding inputting an input signal into a filter having a predeterminedpassband, obtaining an superfluous signal of the passband through thefilter, and obtaining a target signal by subtracting the unnecessarysignal from the input signal by inputting the input signal and theunnecessary signal into a subtractor.

The filter may be a low frequency band pass filter.

The filter may be an infinite impulse response (IIR) filter.

The input signal input into the subtractor may be a signal obtained bycompensating for a time delay in obtaining the unnecessary signal.

The input signal may be a signal obtained by subtracting an estimateddirect current (DC) offset from a raw signal.

The signal processing method may further include determining whether acompensation for the DC offset is to be performed on the target signal,and performing the compensation for the DC offset on the target signalbased on a result of the determining.

The determining may include determining that the compensation for the DCoffset is performed in response to the target signal having a frequencylower than a predetermined frequency, and that the compensation for theDC offset is not performed in response to the target signal having thefrequency higher than the predetermined frequency.

In accordance with another embodiment, there is provided a signalfiltering apparatus including a filter having a predetermined passband,and a subtractor configured to output a target signal obtained bysubtracting an unnecessary signal from the input signal, wherein aninput signal and the unnecessary signal of the passband obtained byapplying the input signal to the filter are input into the subtractor.

The input signal may be a biosignal on which preprocessing is performed.

The preprocessing may be subtracting a direct current (DC) offset.

The unnecessary signal may include a DC component and a signalcorresponding to a band of a frequency lower than a predetermined cutofffrequency.

In accordance with still another embodiment, there is provided a signalprocessing method including estimating a direct current (DC) offset froma raw signal, generating an input signal by subtracting the DC offsetfrom the raw signal, and obtaining a target signal by subtracting anunnecessary signal of a predetermined passband by inputting the inputsignal into a filter having the predetermined passband.

The obtaining may include obtaining the unnecessary signal through thefilter, and obtaining the target signal by subtracting the unnecessarysignal from the input signal by inputting the input signal and theunnecessary signal into a subtractor.

The input signal input into the subtractor may be a signal obtained bycompensating for a time delay in obtaining the unnecessary signal.

The signal processing method may further include determining whether acompensation for the DC offset is to be performed on the target signal,and performing the compensation for the DC offset on the target signalbased on a result of the determining.

In accordance with yet another embodiment, there is provided a signalprocessing apparatus including a direct current (DC) offset subtractorconfigured to estimate a DC offset from a raw signal and output an inputsignal by subtracting the DC offset from the raw signal, and a filteringunit configured to output a target signal by subtracting an unnecessarysignal of a predetermined passband from the input signal.

The signal processing apparatus may further include a DC offsetcompensator configured to determine whether a compensation for the DCoffset is to be performed on the target signal and perform thecompensation for the DC offset on the target signal based on a result ofthe determining.

The DC offset compensator may determine that the compensation for the DCoffset is performed in response to the target signal having a frequencylower than a predetermined frequency, and that the compensation for theDC offset is not performed in response to the target signal having thefrequency higher than the predetermined frequency.

The filtering unit may include a filter having a predetermined passband,and a subtractor configured to input the input signal and theunnecessary signal obtained by applying the input signal to the filterand output the target signal obtained by subtracting the unnecessarysignal.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a method of signalprocessing.

FIG. 2 illustrates an example of a configuration of a signal filteringapparatus.

FIG. 3 illustrates an example of a configuration of a signal filteringapparatus.

FIG. 4 is a diagram illustrating an example of an input signal, ansuperfluous signal, and a target signal.

FIG. 5 is a diagram illustrating an example of a signal processingmethod.

FIG. 6 is a diagram illustrating an example of a configuration of asignal processing apparatus.

FIG. 7 illustrates an example of a configuration of a signal processingapparatus.

FIG. 8 illustrates an example of a configuration of a signal processingapparatus.

Throughout the drawings and the detailed description, unless otherwisedescribed or provided, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures. Thedrawings may not be to scale, and the relative size, proportions, anddepiction of elements in the drawings may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent to one of ordinary skill inthe art after a full understanding of the present disclosure. Thesequences of operations described herein are merely examples, and arenot limited to those set forth herein, but may be changed as will beapparent to one of ordinary skill in the art, with the exception ofoperations necessarily occurring in a certain order. Also, descriptionsof functions and constructions that are well known to one of ordinaryskill in the art may be omitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

Specific structural or functional descriptions of examples provided inthe present disclosure are exemplary to merely describe the examples.The examples may be modified and implemented in various forms, and thescope of the examples is not limited to the descriptions provided in thepresent specification.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement. As used herein, the term “and/or,” includes any and allcombinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected,” or “coupled,” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected,” or “directly coupled,” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between,” versus “directly between,” “adjacent,” versus“directly adjacent,” etc.).

As used herein, the singular forms “a,” “an,” and “the,” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

An example of a signal filtering and signal processing apparatus may beimplemented as a part of various types of products, such as, forexample, personal computers, laptop computers, tablet computers, smartphones, mobile devices, televisions, smart home appliances, intelligentvehicles, kiosks, home appliances, content players, communicationsystems, image processing systems, graphics processing systems, wearabledevices (such as, for example, a ring, a watch, a pair of glasses,glasses-type device, a bracelet, an ankle bracket, a belt, a necklace,an earring, a headband, a helmet, a device embedded in the cloths), orany other consumer electronics/information technology (CE/IT) device.For example, the examples are applicable to user recognition by a smartphone, a mobile device, and a smart home system. The examples areapplicable to a payment service requiring user recognition. Further, theexamples are applicable to an intelligent automobile system whichautomatically starts up an engine after recognizing a user.

FIG. 1 is a diagram illustrating an example of a signal processingmethod. The signal processing method of FIG. 1 is performed by a signalprocessing apparatus including at least one processor. The operations inFIG. 1 may be performed in the sequence and manner as shown, althoughthe order of some operations may be changed or some of the operationsomitted without departing from the spirit and scope of the illustrativeexamples described. Many of the operations shown in FIG. 1 may beperformed in parallel or concurrently.

To subtract a signal from a raw signal or to subtract remainingcomponents except for a desired signal, various filtering schemes may beapplied. For example, the filtering scheme may subtract an interferencesignal existing in a neighboring band except for a signal in a desiredband from a reception signal in a communication system. In anotherexample, the the filtering scheme may subtract a component of afrequency band other than a frequency band of interest from a biosignalmeasured through a measuring apparatus.

A biosignal refers to a signal essentially generated from body activityof a creature, such as, for example, electrocardiography (ECG),photoplethysmogram (PPG), ballistocardiogram (BCG), blood oxygensaturation level (SpO₂), electrodermal activity (EDA),electroencephalography (EEG), electrooculography (EOG), galvanic skinresponse (GSR), and electromyography (EMG). Based on an analysis of thebiosignal obtained from a biosignal sensor various pieces of informationassociated with a heartbeat may be obtained and differing health relatedvalues of an individual may be estimated from the ECG or the PPG signal.An EMG sensor may measure a condition change of muscles by sensing acurrent flowing in the muscles. Monitoring an amount of current in themuscles based on the EMG may be done for a muscle strengthening programand an EMG sensor may be used to recognize a movement by classifyingpatterns of contraction and relaxation of different muscles of a body.

A PPG signal includes an alternating current (AC) component, a directcurrent (DC) component, a component close to a DC, and an additive whiteGaussian noise (AWGN) of an arterial signal. The DC component includes asystem bias, an ambient light, a vein PPG, and respiration, and the DCcomponent may be distributed in a frequency band less than 0.3 hertz(Hz). Since a signal of the AC component from which the DC component anda noise signal of the PPG signal are subtracted is distributed in afrequency band from 0.3 to 50 Hz, a process of subtracting a signal of afrequency band greater than 50 Hz and a signal within a frequency bandfrom 0 to 0.3 Hz may be required. To subtract a low frequency signal ofa narrow band from 0 to 0.3 Hz, an elaborate filter may be designed. Ina process of subtracting a signal of the band, a signal delay or signaldistortion may occur.

A digital filter may be designed by setting a passband or a cutofffrequency and defining a filter value based on filter types and filterorders according to use or purpose. The designed digital filter may beused to extract a desired signal by subtracting a noise from a rawsignal. For example, the digital filter may be a finite impulse response(FIR) filter, an infinite impulse response (IIR) filter, and a zerophase filter (ZPF). The digital filter may be used to extract a signalof a band of interest or to subtract a noise from a raw signal. The FIRfilter may require a design of a filter having a length greater than orequal to thousands of taps to subtract a signal of a frequency bandhaving a narrow interval. Thus, a signal delay may be unavoidable andcalculation complexity may increase in a filtering process, so that theFIR filter is not appropriate for a wearable device to process abiosignal. In response to the IIR filter being used instead of using theFIR filter, the calculation complexity may decrease, but distortion mayoccur in a signal band. Signal filtering and processing methods andapparatuses are disclosed to apply filtering technology for subtractingthe noise from the raw signal and to extract the signal of the band ofinterest in the wearable device. In another embodiment, a filteringscheme having low calculation complexity to effectively subtract thenoise and to minimize the distortion of the signal is disclosed.

In an example, in 101, an input signal is sent into a filter having apassband. In an example, the passband of the filter may bepredetermined. In an example, the passband of the filter may be definedin advance to include a frequency band except for band of interest.

In an example, the filter may be a low frequency band pass filter. Inthis example, the band of interest may be a high frequency band. Inanother example, the filter may be a high frequency band pass filter. Inthis example, the band of interest may be a low frequency band. Thefilter into which the input signal is input may be designed to be a bandpass filter, and the passband of the filter may be variously applicablebased on design methods and design conditions. The filter may bedesigned to be an IIR or an FIR, but the filter is not limited thereto.For example, in response to the input signal being a PPG signal, the IIRfilter may be applied as the low frequency band pass filter to subtracta signal of a low frequency band from 0 to 0.3 Hz. However, this is onlyan example, and a design of the filter may be variously changed andapplied based on the band of interest.

In an example, in 102, a superfluous signal of the passband of the inputsignal is obtained through the filter into which the input signal isinput. The superfluous signal may be a signal that is to be subtractedfrom the input signal.

In an example, in 103, the input signal and the superfluous signal areinput into a subtractor, and a target signal is obtained by subtractingthe superfluous signal from the input signal based on an output of thesubtractor. In this example, a signal of a band of interest to beobtained from an input signal is referred to as a target signal and asignal subtracted from the input signal to obtain the target signal isreferred to as a superfluous signal. The superfluous signal includes asignal to be subtracted from the input signal, for example, a noise, asystem bias and an ambient light. An operation of subtracting thesuperfluous signal from the input signal may be controlled by aprocessor, for example.

In an example, the input signal input into the subtractor is a signalobtained by compensating for a time delay in obtaining the superfluoussignal. In response to the time delay in applying the input signal tothe filter and obtaining the superfluous signal is delayed, acompensation for the delayed time may be performed on the input signal,and the superfluous signal may be subtracted from the input signal onwhich the compensation is performed.

In an example, the input signal is a signal obtained by subtracting theDC offset from the raw signal. In response to a signal, having a largeDC offset being applied to the filter, a setting time of the signalobtained through filtering may be required. In response to the DC offsetbeing subtracted before the signal that is applied to the filter, thesetting time may be reduced. In response to the DC offset beingestimated from the raw signal and the input signal being obtained bysubtracting the estimated DC offset from the raw signal being applied tothe filter, a setting time of the target signal may be reduced.

In an example, in response to the input signal being the signal obtainedby subtracting the estimated DC offset from the raw signal, acompensation for the DC offset may be performed on the target signal.For example, in response to the target signal having a frequency lowerthan a preset frequency, the compensation for the DC offset is performedon the target signal since the band of interest of the target signalincludes the DC component. In another example, in response to the targetsignal having the frequency higher than the preset frequency, thecompensation for the DC offset is not performed on the target signalsince the DC component is to be excluded from the band of interest ofthe target signal.

FIG. 2 illustrates an example of a configuration of a signal filteringapparatus.

In an example, a signal filtering apparatus 200 includes a filter 201and a subtractor 202. In an example, the filter 201 may have a presetpassband and output a superfluous signal of the passband by filtering aninput signal to the passband.

In an example, the subtractor 202 may receive the input signal and thesuperfluous signal output by the filter 201. The subtractor 202 mayoutput a target signal by subtracting the superfluous signal from theinput signal. In this example, the operation of inputting and outputtinga signal into the filter 201 and the subtractor 202 may be controlled bya processor.

In an example, the input signal may be a raw signal on whichpreprocessing is performed, and the raw signal may include a biosignal.The preprocessing performed on the raw signal may include an operationof subtracting a direct current (DC) offset.

In an example, the DC offset may be estimated from the raw signal, suchas, for example, the ECG, the PPG, and the EMG. The estimated DC offsetmay be subtracted from the raw signal, for example, duringpreprocessing, and may be input into the filter 201. The target signalmay be obtained through the subtractor 202.

FIG. 3 illustrates an example of a configuration of a signal filteringapparatus.

In an example, a band of a signal to be subtracted from an input signalmay be estimated. The input signal may be applied to a filter 301 havingthe estimated band of the signal as a passband. The filter 301 outputs asuperfluous signal of the passband from the input signal.

In response to the superfluous signal being output through the filter301, a propagation delay of the signal may occur. Thus, compensation fora time delay by the filter 301 may be performed on the input signalbefore the superfluous signal is subtracted from the input signal. Adelay compensator 302 performs, on the input signal, the compensationfor a time delay in outputting the superfluous signal obtained by theinput signal passing through the filter 301, and inputs the time-delayedinput signal into an adder-subtractor 303.

The adder-subtractor 303 outputs a target signal by subtracting thesuperfluous signal from the time-delayed input signal using thetime-delayed input signal output from the delay compensator 302 and thesuperfluous signal output from the filter 301.

FIG. 4 is a diagram illustrating an example of an input signal, asuperfluous signal, and a target signal.

In an example, in response to an input signal 401 input into a filter, asuperfluous signal 402 output through a filter, and the superfluoussignal 402 subtracted from the input signal 401, the input signal 401,the target signal 403, and the superfluous signal 402 may be representedas illustrated in the graph of FIG. 4. The graph of FIG. 4 represents anexample in which a target signal 403 is a signal of a high frequencyband. In this example, a signal filtering apparatus may be replaced witha high pass filter (HPF). In response to the target signal 403 being asignal of a low frequency band, the signal filtering apparatus may bereplaced as a low pass filter (LPF). The foregoing may be variouslyapplicable based on a design method.

The superfluous signal 402 is extracted from the input signal 401through a filter having a preset passband of a frequency lower than acutoff frequency. The target signal 403 in a band of interest may beobtained by subtracting the extracted superfluous signal 402 from theinput signal 401.

When the superfluous signal 402 is extracted through the filter havingthe preset passband, the superfluous signal 402 in the passband may beextracted with low calculation complexity where an infinite impulseresponse (IIR) filter is used.

FIG. 5 is a diagram illustrating an example of a signal processingmethod. The method of signal processing of FIG. 5 is performed by asignal processing apparatus including at least one processor. Theoperations in FIG. 5 may be performed in the sequence and manner asshown, although the order of some operations may be changed or some ofthe operations omitted without departing from the spirit and scope ofthe illustrative examples described. Many of the operations shown inFIG. 5 may be performed in parallel or concurrently. In addition to thedescription of FIG. 5 below, the above descriptions of FIGS. 1-4, arealso applicable to FIG. 5, and are incorporated herein by reference.Thus, the above description may not be repeated here.

In 501, a direct current (DC) offset is estimated from a raw signal. Inan example, in response to the raw signal of which the DC offset isgreat being input into a filter, a setting time greater than or equal toseconds for converging a signal output from the filter having a presetpassband may be required.

In 502, the input signal obtained by subtracting the estimated DC offsetfrom the raw signal is generated. The setting time of the filter may bereduced in response to the input signal obtained by subtracting the DCoffset from the raw signal being applied to the filter before the rawsignal is applied to the filter.

In 503, a target signal is obtained by subtracting a superfluous signalof the passband by inputting the input signal into the filter having thepassband. In an example, the superfluous signal may be obtained from theinput signal input through the filter having the passband, and the inputsignal and the superfluous signal may be input into a subtractor. Thetarget signal may be obtained by subtracting, by the subtractor, thesuperfluous signal from the input signal, and the input signal input tothe subtractor may be a signal obtained by compensating for a time delayin obtaining the superfluous signal.

In an example, a compensation for the DC offset may be performed on thetarget signal based on determining whether the compensation for theestimated DC offset is to be performed on the target signal. Forexample, it may be determined that the compensation for the DC offset isto be performed in response to the target signal having a frequencylower than a predetermined frequency, and it may be determined that thecompensation for the DC offset is to be performed in response to thetarget signal having the frequency higher than the predeterminedfrequency. The examples described above with reference to FIGS. 1through 4 may be applicable to an operation of subtracting thesuperfluous signal from the input signal. However, the operation ofsubtracting the superfluous signal from the input signal is not limitedthereto.

FIG. 6 illustrates an example of a configuration of a signal processingapparatus in accordance with an embodiment.

A signal processing apparatus 600 includes a direct current (DC) offsetsubtractor 601, a filtering unit 602, and a DC offset compensator 603.

The DC offset subtractor 601 estimates a DC offset from a raw signal andoutputs an input signal by subtracting the DC offset from the rawsignal. In an example, the DC offset is estimated by inquiring aboutinformation known in advance or an operation of estimating a value ofthe DC offset from the raw signal.

The filtering unit 602 outputs a target signal by subtracting asuperfluous signal of a passband from the input signal. Although notillustrated in FIG. 6, the filtering unit 602 may include a filterhaving a passband and a subtractor. In an example, the passband may bepreset. The filter of the filtering unit 602 may extract the superfluoussignal of the passband with respect to an applied input signal andoutput the extracted superfluous signal. The subtractor of the filteringunit 602 may receive the superfluous signal and the input signal, andoutput the target signal by subtracting the superfluous signal from theinput signal. The input signal input into the subtractor may be a signalobtained by compensating for a time delay in passing through thefiltering unit 602.

The DC offset compensator 603 determines whether to perform compensationfor the DC offset on the target signal and performs the compensation forthe DC offset based, if desired. The DC offset compensator 603 performsthe compensation for the DC offset in response to the target signalhaving a frequency lower than a preset frequency, and the DC offsetcompensator 603 does not perform the compensation for the DC offset inresponse to the target signal having the frequency higher than thepreset frequency.

FIG. 7 illustrates an example of a configuration of a signal processingapparatus.

Referring to FIG. 7, a direct current (DC) offset estimator 701 receivesa raw signal, estimates a DC offset from the raw signal, outputs theestimated DC offset, and inputs the output DC offset into anadder-subtractor 702. The adder-subtractor 702 receives the raw signaland the DC offset, and outputs a signal by subtracting the DC offsetfrom the raw signal. The signal output by the adder-subtractor 702 isreferred to as an input signal.

A filtering unit 703 extracts a superfluous signal of a passband fromthe input signal, which is output from the adder-subtractor 702. Thefiltering unit 703 outputs the target signal obtained by subtracting thesuperfluous signal from the input signal. The filtering unit 703 inputsthe output target signal to an adder-subtractor 705.

A DC offset compensation determiner 704 receives information on theestimated DC offset and the raw signal from the DC offset estimator 701and determines whether a compensation for the DC offset is to beperformed on the target signal is required. In response to the targetsignal being a signal corresponding to a band of a frequency higher thana predetermined frequency, the DC offset compensation determiner 704inputs the DC offset into the adder-subtractor 705 since thecompensation for the DC offset is required. In response to the targetsignal being a signal corresponding to the band of the frequency lowerthan the predetermined frequency, the DC offset compensation determiner704 does not input the DC offset to the adder-subtractor 705 since thecompensation for the DC offset is not required.

The adder-subtractor 705 outputs the target signal on which thecompensation for the DC offset is performed using the target signaloutput from the filtering unit 703 and the DC offset output from the DCoffset compensation determiner 704.

FIG. 8 illustrates still an example of a configuration of a signalprocessing apparatus.

Referring to FIG. 8, a direct current (DC) offset subtractor 801receives a raw signal, subtracts an estimated DC offset from the rawsignal, and outputs an input signal. The DC offset subtractor 801 inputsthe input signal into a filter 802 and a delay compensator 803.

The filter 802 has a passband. The filter 802 outputs a superfluoussignal of the input signal.

The delay compensator 803 performs time delay on the input signal outputfrom the DC offset subtractor 801. The delay compensator 803 performs,on the input signal, a compensation for a time delay in extracting thesuperfluous signal through the filter 802. The delay compensator 803outputs the input signal on which the compensation for the time delay isperformed.

An adder-subtractor 804 outputs a target signal by subtracting thesuperfluous signal output from the filter 802 from the input signaloutput from the delay compensator 803.

The DC offset compensation determiner 805 receives information on theraw signal and the DC offset estimated from the DC offset subtractor801, determines whether the compensation for the DC offset is to beperformed on the target signal, and outputs the DC offset requiring thecompensation based on the determination. An adder-subtractor 806receives the target signal and the DC offset output from the DC offsetcompensation determiner 805, performs the compensation for the DC offseton the target signal, and outputs the target signal on which thecompensation for the DC offset is performed.

As a non-exhaustive illustration only, the signal filtering apparatus200 and 600 may refer to or be implement in mobile devices such as, forexample, a mobile phone, a cellular phone, a smart phone, a wearablesmart device (such as, for example, a ring, a watch, a pair of glasses,glasses-type device, a bracelet, an ankle bracket, a belt, a necklace,an earring, a headband, a helmet, a device embedded in the cloths), apersonal computer (PC), a laptop, a notebook, a subnotebook, a netbook,or an ultra-mobile PC (UMPC), a tablet personal computer (tablet), aphablet, a mobile internet device (MID), a personal digital assistant(PDA), an enterprise digital assistant (EDA), a digital camera, adigital video camera, a portable game console, an MP3 player, aportable/personal multimedia player (PMP), a handheld e-book, an ultramobile personal computer (UMPC), a portable lab-top PC, a globalpositioning system (GPS) navigation, a personal navigation device orportable navigation device (PND), a handheld game console, an e-book,and devices such as a high definition television (HDTV), an optical discplayer, a DVD player, a Blue-ray player, a setup box, robot cleaners, ahome appliance, content players, communication systems, image processingsystems, graphics processing systems, other consumerelectronics/information technology (CE/IT) device, or any other devicecapable of wireless communication or network communication consistentwith that disclosed herein. The mobile device may be implemented in asmart appliance, an intelligent vehicle, or in a smart home system.

The signal filtering apparatus 200 and 600 may also be implemented as awearable device, which is worn on a body of a user. In one example, awearable device may be self-mountable on the body of the user, such as,for example, a watch, a bracelet, or as an eye glass display (EGD),which includes one-eyed glass or two-eyed glasses. In anothernon-exhaustive example, the wearable device may be mounted on the bodyof the user through an attaching device, such as, for example, attachinga smart phone or a tablet to the arm of a user using an armband,incorporating the wearable device in a cloth of the user, or hanging thewearable device around the neck of a user using a lanyard.

The apparatuses, units, modules, devices, and other componentsillustrated in FIGS. 2-3 and 6-8 that perform the operations describedherein with respect to FIGS. 1 and 5 implemented by hardware components.Examples of hardware components include controllers, sensors,generators, drivers, and any other electronic components known to one ofordinary skill in the art. In one example, the hardware components areimplemented by one or more processors or computers. A processor orcomputer is implemented by one or more processing elements, such as anarray of logic gates, a controller and an arithmetic logic unit, adigital signal processor, a microcomputer, a programmable logiccontroller, a field-programmable gate array, a programmable logic array,a microprocessor, or any other device or combination of devices known toone of ordinary skill in the art that is capable of responding to andexecuting instructions in a defined manner to achieve a desired result.In one example, a processor or computer includes, or is connected to,one or more memories storing instructions or software that are executedby the processor or computer. Hardware components implemented by aprocessor or computer execute instructions or software, such as anoperating system (OS) and one or more software applications that run onthe OS, to perform the operations described herein. The hardwarecomponents also access, manipulate, process, create, and store data inresponse to execution of the instructions or software. For simplicity,the singular term “processor” or “computer” may be used in thedescription of the examples described herein, but in other examplesmultiple processors or computers are used, or a processor or computerincludes multiple processing elements, or multiple types of processingelements, or both. In one example, a hardware component includesmultiple processors, and in another example, a hardware componentincludes a processor and a controller. A hardware component has any oneor more of different processing configurations, examples of whichinclude a single processor, independent processors, parallel processors,single-instruction single-data (SISD) multiprocessing,single-instruction multiple-data (SIMD) multiprocessing,multiple-instruction single-data (MISD) multiprocessing, andmultiple-instruction multiple-data (MIMD) multiprocessing.

The methods illustrated in FIGS. 1 and 5 that perform the operationsdescribed herein are performed by computing hardware as described aboveexecuting instructions or software to perform the operations describedherein.

Instructions or software to control a processor or computer to implementthe hardware components and perform the methods as described above arewritten as computer programs, code segments, instructions or anycombination thereof, for individually or collectively instructing orconfiguring the processor or computer to operate as a machine orspecial-purpose computer to perform the operations performed by thehardware components and the methods as described above. In one example,the instructions or software include machine code that is directlyexecuted by the processor or computer, such as machine code produced bya compiler. In another example, the instructions or software includehigher-level code that is executed by the processor or computer using aninterpreter. Programmers of ordinary skill in the art can readily writethe instructions or software based on the block diagrams and the flowcharts illustrated in the drawings and the corresponding descriptions inthe specification, which disclose algorithms for performing theoperations performed by the hardware components and the methods asdescribed above.

The instructions or software to control a processor or computer toimplement the hardware components and perform the methods as describedabove, and any associated data, data files, and data structures, arerecorded, stored, or fixed in or on one or more non-transitorycomputer-readable storage media. Examples of a non-transitorycomputer-readable storage medium include read-only memory (ROM),random-access memory (RAM), flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs,CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, BD-ROMs,BD-Rs, BD-R LTHs, BD-REs, magnetic tapes, floppy disks, magneto-opticaldata storage devices, optical data storage devices, hard disks,solid-state disks, and any device known to one of ordinary skill in theart that is capable of storing the instructions or software and anyassociated data, data files, and data structures in a non-transitorymanner and providing the instructions or software and any associateddata, data files, and data structures to a processor or computer so thatthe processor or computer can execute the instructions. In one example,the instructions or software and any associated data, data files, anddata structures are distributed over network-coupled computer systems sothat the instructions and software and any associated data, data files,and data structures are stored, accessed, and executed in a distributedfashion by the processor or computer.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not forpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner, and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. A photoplethysmogram (PPG) signal processingmethod, comprising: obtaining a PPG signal through a biosignal sensor;generating an input signal by subtracting a DC offset from the PPGsignal; inputting the input signal to a first processing path and asecond processing path, wherein the first processing path comprises alow pass filter that has a cutoff frequency and the second processingpath comprises a delay compensator configured to compensate for a timedelay related to the low pass filter; and obtaining a target signal bysubtracting a signal obtained from the first processing path from asignal obtained from the second processing path.
 2. The method of claim1, wherein the target signal has a frequency higher than 0.3 hz.
 3. Themethod of claim 1, wherein the target signal has a frequency lower than50 hz.
 4. A wearable device, comprising: a sensor configured to measurea PPG signal; and a signal processing apparatus comprising: anadder-subtractor configured to generate a input signal by subtracting aDC offset from the measured PPG signal, and configured to input theinput signal to a first processing path and a second processing path; alow pass filter disposed in the first processing path, and configured tohave a cutoff frequency; a delay compensator disposed in the secondprocessing path, and configured to compensate for a time delay relatedto the low pass filter; and a subtractor configured to obtain a targetsignal by subtracting a signal obtained from the first processing pathfrom a signal obtained from the second processing path.
 5. The wearabledevice of claim 4, wherein the target signal has a frequency higher than0.3 hz.
 6. The wearable device of claim 4, wherein the target signal hasa frequency lower than 50 hz.